This allows trailing commas in multi-line arg lists.
Minor, but we might as well keep our formatting current with regard to
our minimum supported Python version.
Signed-off-by: Dan Callahan <danc@element.io>
This implements a more standard API for instantiating a homeserver and
moves some of the dependency injection into the test suite.
More concretely this stops using `setattr` on all `kwargs` passed to `HomeServer`.
